MOVEMENTS IN THE VISUAL CELLS 143 



My first effort, therefore, was to repeat Herzog's work using 

 apparatus and methods that essentially agreed with his, in 

 order to ascertain whether identical results would be reahzed. 

 If the movements of the frog's retinal pigment are really ex- 

 ceptional among other lower vertebrates, such responses have 

 considerable theoretical as well as incidental interest. 



The following apparatus was de\nsed. A cubical cage, made 

 of fine wire netting with a cover of the same material, was sup- 

 ported by uprights inside a large battery jar which was fittcul 

 with a glass cover perforated by a small hole to allow slow dif- 

 fusion of air. The wire cage, made to receive the frog, did not 

 come in contact with any part of the surrounding glass receiver 

 which was to serve as a constant temperature chamber. The 

 glass receiver sat upon a platform in a large cyhndrical metal 

 tank. A thermometer passed through the cover of the tank 

 and also through the cover of the temperature chamber into 

 that chamber itself. A funnel connected with a rubber tube 

 to exclude light was fitted into the cover of the tank and served 

 for introducing water into the tank. 



Tests were conducted in the following way. A dark-adapted 

 frog was wiped dry and plac(>d within the wire cage^" inside the 

 constant temperature chamber. Previously the chambei- had 

 been brought to the desired temperature by one of two simple 

 methods. If the efTect of heating was to be studied, the metal 

 tank was partially filled with watei- at the appropriate temperature 

 and the whole system allowi^l to adjust itself until the ther- 

 mometer ins'de the constant temjierature chamber registered 

 the required degree of warmth. After the frog had been in- 

 troduced, the temperature could be regulated without opening 

 the apparatus by admitting warmer water through the funnc^l 

 and drawing off an equivalent amount from the bottom of the 

 tank. If, on the other hand, a temperature near the freezing 



'" Herzog lays much stress on the facts that the animaTs body was never in 

 contact with solids other than the wires of the cage, and that the body was always 

 wiped free from secretions or excretions at the commencement of an experiment. 

 He seems to fear lest there should be a chemical stimulation due to heated secre- 

 tions or excretions that would affect the results in case these precautions were 

 not followed. 



